Abstract

The velocity distribution of a beam of 50-volt electrons issuing from a hole 0.022 cm in diameter in a copper plate 0.02 cm thick has been measured. Seventy percent of the electrons were found to retain approximately their initial velocity. By coating the sides and edges of the hole with lampblack 95% of the electrons were transmitted without appreciable energy loss. Similar results were obtained with grids of 100 mesh copper gauze.